c - Understanding input/output operands in GCC inline assembly syntax -

-

as part of writing os, implementing interrupt handling , i/o functions inb , outb.

i had learn writing inline assembly in gcc , read lot online. based on understanding, wrote own code. meanwhile, looked linux's implementation of functions /usr/include/sys/io.h. outb:

static __inline void outb (unsigned char __value, unsigned short int __port) {   __asm__ __volatile__ ("outb %b0,%w1": :"a" (__value), "nd" (__port)); }

here questions:

  • the gcc manual says "n"

unsigned 8-bit integer constant (for in , out instructions).

but here __port unsigned short int believe 16 bits. how decided portion of 16 bits used in inline assembly ?

  • this understanding of how works - value of __port used directly (because of "n") constant in place of %w1. value of __value copied eax. %bo replaced %al. instruction executed. correct ?

  • how decided of "n" or "d" use second operand ? there preference order ?

  • what difference make if don't use "n" ? wouldn't using "d" better, since 16 bits ?

  • if omitted "n", correct value of __port copied edx , %w1 replaced edx ?

i may mistaken, understanding "nd" means use either n or d, @ compiler's preference. if value not known constant fits in 8 bits, n not satisfiable, compiler has no choice use d. when value compile-time constant , value fits in 8 bits, using 8-bit immediate preferable wasting register.


Comments

Post a Comment

Popular posts from this blog

C# random value from dictionary and tuple -

-
i have following code, , need random item contains string "region_1" dictionary. public static dictionary<int, tuple<string, int, currencytype>> itemarray = new dictionary<int, tuple<string, int, currencytype>>() { { 0xb3e, new tuple<string, int, currencytype>("region_1", 1500, currencytype.fame) } }; public static int generateitemid(string shopid) { var generateditem = itemarray.elementat(new random().next(0, itemarray.count)).key; } how select this? it's not possible efficiently... first create static random @ class level... prevent non-random behaviour if run query on short period of time... (it's seeded discrete clock) static random rnd = new random(); then: var item = itemarray.values .where(t => t.item1 == shopid) .orderby(_ => rnd.next()) .firstordefault()
Read more

.htaccess - htaccess convert request to clean url and add slash at the end of the url -

-
ok , searched more 4 days , more 20 posts here in stach or in websites without kind of success first here htaccess file rewriteengine on rewriterule ^([a-za-z0-9_]+)/?$ index.php?page=$1 [nc] rewriterule ^([a-za-z0-9_]+)\/([a-za-z0-9_]+)\/?$ index.php?page=$1&action=$2 [nc] i tried many codes 1 worked me can call request , works me www.example.com/pagename => www.example.com/index.php?page=pagename here questions , please provide me information "in detail" understand code well 1- how convert request automatically www.example.com/index.php?page=pagename www.example.com/pagename 2- if tried add slash @ end shows me page without images or styling mean www.example.com/pagename => works www.example.com/pagename/ => doesn't work that's :) for first part need 301 rule this: rewritecond %{the_request} /index\.php\?page=([^\s&]+) [nc] rewriterule ^ /%1? [r=301,l] for second part use absolute path in css, js, images files r...
Read more

cgi - How do I interpret URLs without extension as files rather than missing directories in nginx? -

-
so i'm trying install zoneminder , have run under nginx, has few compiled files need run using fast-cgi. these files lack extension. if file has extension, there no issue , nginx interprets file , return 404 if can't find it. if has no extension, assume it's directory , return 404 when can't find sort of index page. here have now: # security camera domain. server { listen 888; server_name mydomain.com; root /srv/http/zm; # enable php support. include php.conf; location / { index index.html index.htm index.php; } # enable cgi support. location ~ ^/cgi-bin/(.+)$ { alias /srv/cgi-bin/zm/; fastcgi_pass unix:/run/fcgiwrap.sock; fastcgi_param script_filename $document_root/$1; include fastcgi.conf; } } the idea is, under cgi-bin directory goes through fastcgi pipe. any idea on howi can fix this? upon closer inspection, realized zoneminder has 2 cgi sc...
Read more